The purpose of this application, resubmitted with substantial changes reflecting the thoughtful reviewer comments from the second round of submission, is to improve understanding of longitudinal changes in relationship formation activity and risk behaviors that lead to the transmission of human immunodeficiency virus (HIV) and other sexually transmitted diseases (STDs). We will examine data collected in a proposed fourth wave of a unique longitudinal data set, the National Survey of Adolescent Males (NSAM). This survey, a nationally representative sample of 1,880 men who were 15 to 19 years old in 1988, has interviewed men three times already about their sexual and protective behaviors in 1988,1990-91, and 1995. In 2006 the respondents will be approximately 32-37. The proposed study builds on our prior and ongoing investigations concerning HIV/STD risk and protective behaviors of young American males, and it will examine shifts in these behaviors across their life courses. We will identify trajectories of risk behaviors among individuals and subgroups of men as they pass from adolescence into adulthood. Longitudinal analyses will provide a fresh way to look at a variety of transitions into and out of risk behaviors, including changes in partnering and protective behaviors. Of particular interest is the identification of groups of men who either persistently exhibit high-risk behavior or exhibit shifts into or away from high risk behavior. The specific aims of this application are to: 1. Conduct a fourth round of the NSAM to determine the covariates and prevalence of behaviors among young men (ages 32-37) that put them at risk of HIV/STD. 2. Describe the progression of risk behaviors across the life course as men move from adolescence into adulthood. 3. Examine factors associated with transitions into and out of high risk behaviors. 4. Prepare a documented public use tape for the fourth round of data which can be linked to the previous waves of data.